Copper alloy for electronic materials used for various electronic components such as connector, switch, relay, pin, terminal, lead frame and so forth are required to satisfy both of high strength and high electrical conductivity (or heat conductivity) as basic characteristics. In recent years, with rapid progress in higher integration, miniaturization and thinning of the electronic components, requirements for the copper alloy used for the components for electronic instruments have been growing more and more severe.
In consideration of high strength and high electrical conductivity of copper alloys for electronic materials, the use of precipitation hardening copper alloys has increased, in place of traditional solid solution strengthened copper alloys such as phosphor bronze and brass. In the precipitation hardening copper alloys, age hardening of supersaturated solid solution after solution treatment facilitates uniform dispersion of fine precipitates and thus an increase in strength of the alloys. It also leads to a decrease in amount of solute elements in copper matrix and thus an improvement in electrical conductivity. The resulting materials have superior mechanical properties such as strength and spring properties, as well as high electrical and thermal conductivities.
Among precipitation hardening copper alloys, Cu—Ni—Si-based copper alloy generally called “Corson-based alloy” is a representative copper alloy having all of relatively high electrical conductivity, strength, and bendability, and is one of the alloys having been developed vigorously in the related industry. The strength and electrical conductivity of this copper alloy can be improved, by allowing fine particles of Ni—Si-based intermetallic compound to precipitate in a copper matrix.
A Cu—Ni—Si-based alloy generally called Corson-based copper alloy has conventionally been known as a representative copper alloy having all of relatively high electrical conductivity, strength and bendability. The strength and electrical conductivity of this copper alloy may be improved, by allowing fine particles of Ni—Si-based intermetallic compound to precipitate in a copper matrix. It is, however, difficult for the Cu—Ni—Si-based alloy to achieve an electrical conductivity of 60% IACS or higher, while keeping high strength. For this reason, Cu—Co—Si-based alloy now attracts attention. The Cu—Co—Si-based alloy is advantageous in that electrical conductivity may be grown higher than that of the Cu—Ni—Si-based copper alloy, by virtue of its lower solute content of cobalt silicide (Co2Si).
Processes largely influential to characteristics of the Cu—Co—Si-based copper alloy are exemplified by solution treatment, ageing, and final rolling. Among others, ageing is one of the processes most influential to distribution and particle size of precipitates of cobalt silicide.
Patent Document 1 (Japanese Laid-Open Patent Publication No. 2008-56977) describes Cu—Co—Si-based alloy examined with respect to not only copper alloy composition, but also particle size and total amount of inclusion which precipitates in the copper alloy, wherein the alloy is aged, after solution treatment, at 400° C. or above and 600° C. or below for 2 hours or longer and 8 hours or shorter. According to the document, the particle size of inclusion precipitated in the copper alloy is reportedly adjusted to 2 μm or smaller, and the content of the inclusion of 0.05 μm or larger and 2 μm or smaller in the copper alloy is adjusted to 0.5% by volume or below.
Patent Document 2 (Japanese Laid-Open Patent Publication No. 2009-242814) exemplifies a Cu—Co—Si-based alloy as a precipitation hardening copper alloy capable of achieving an electrical conductivity of as high as 50% IACS or more which is not readily achievable by the Cu—Ni—Si-based alloy. The document describes the ageing proceeded at 400 to 800° C. for 5 seconds to 20 hours. The document also specifies state of diffusion of the second phase, from the viewpoint of controlling crystal grain size, specifically describing that the second phase particles reside on grain boundary at a density of 104 to 108 particles/mm2, and that r/f value of 1 to 100, wherein the r/f value is defined as a ratio of diameter r (in μm) of all second phase particles which reside in the crystal grains and on the grain boundary, to volume fraction f of the particles.
Patent Document 3 (WO2009-096546) describes a Cu—Co—Si-based alloy characterized in that the size of precipitate, containing both of Co and Si, is 5 to 50 nm. According to the description, ageing after solution treatment for recrystallization is preferably proceeded at 450 to 600° C. for 1 to 4 hours.
Patent Document 4 (WO2009-116649) describes a Cu—Co—Si-based alloy having excellent strength, electrical conductivity, and bendability. According to Examples described in the document, the ageing is proceeded at 525° C. for 120 minutes, rate of heating from room temperature up to the maximum temperature falls in the range from 3 to 25° C./min, and rate of cooling in a furnace down to 300° C. falls in the range from 1 to 2° C./min.